What’s the Difference Between Line and Mic Levels?

Are you confused by line level versus mic level? Well, you’re not alone. We’re often asked to explain the difference. Simply stated, these both refer to the voltage level of an audio signal.

Wired and wireless microphones are typically connected to mic-level inputs, whereas most other audio devices use line level. (We’ll get to instrument- and speaker-level signals in a minute.) The voltage of each signal type varies significantly, however, making it important to know how they differ.

What is mic level?

A mic-level or microphone-level signal describes the voltage generated by a microphone when it picks up sound, typically just a few thousandths of a volt. This voltage varies in response to changes in sound level and distance. Of the four main types of audio signals, mic level is the weakest and requires a pre-amplifier to bring it up to line level. Microphone levelis usually specified between -60 and -40 dBu. (dBu and dBV are decibel measurements relative to voltage.)

Several different types of devices are used to boost microphone levels to line–level signals. Mixers are probably the most popular piece of equipment, since they can also combine multiple signals together into a single output. But preamplifiers and mic-to-line amplifiers do the job just as well and are available as single-channel or multi-channel devices.

What is line level?

A line-level signal is approximately one volt, or about 1,000 times as strong as a mic-level signal, so the two do not ordinarily use the same input. This signal travels from your pre-amp to the amplifier that powers your speakers.

The other two types of audio signals you’ll run into are instrument and speaker levels. Like mic-level signals, instrument-level signals (such as an electric guitar or bass) require preamplification to bring them up to line level. Post-amplification speaker-level signals are even higher in voltage than line level and require speaker cables for safe signal transfer.

Matching Levels

It’s crucial to match a device to the correct input, since there’s no real technical tolerance for mistakes. For example:

Connecting a microphone to a line-level input will result in almost no sound at all, because the mic-level signal is too weak to drive the line-level input

Connecting a line-level source to a mic-level input will cause the sound to be loud and distorted because the line-level signal is much stronger than what the mic input will accept. (Note: Inputs and outputs on some higher-end mixers are mic and line level switchable.)

Helpful Hints

Don’t assume that the levels match just because one connector fits properly with another. Inputs are generally very clearly marked.

If there is only a mic input on a device (for example, a digital recorder or a computer) and you need to connect a line level device to it, you can reduce the voltage by using an attenuator or a DI (Direct Injection) box, available at most music stores. There are even cable versions with built-in resistors that accomplish the same task.

Different wireless receivers have different output levels. This is true for the Shure line of products and with most competitor brands. Consult the user guide of each wireless receiver to determine its output signal level. Miclevel can vary as much as 20 dB between different receivers.

Justin Boller is an Applications Engineer at Shure Incorporated by day, assisting customers with product selection, system design, and troubleshooting. By night he is a professional musician, performing on tuba, electric and acoustic bass, guitar, trombone, and other instruments in various musical ensembles. He holds a B.S. in Music and an M.S. in Arts Technology from Illinois State University. When there's any spare time, he also enjoys tinkering with electronics, cycling, and cooking on the grill.

This appears to be a list of parameters for a signal processor or digital mixer, which may allow control over how much of a reverb or echo effect enters the signal path, for instance.An HPF (high-pass filter) effectively filters out low frequencies, as another example.

Thank you Justin for a well-written explanation. This always puzzled me, a non-pro musician who likes to record his music. You can tell your marketing department (and your boss) that I will definitely consider Shure products next time I’m shopping. Good people make good products, as one of the other commenters said 🙂

The argument we have in the live sound world often regards using line level output and very little preamp level at the mixer VS mic level output and more preamp gain to reach unity on the mixer meter. I believe in the case of lower grade live sound mixers that gain-to-feedback ratio is reduced by using mic level output. Is this correct?

It depends. I would expect a lower signal-to-noise ratio using “mic” input, since you potentially are adding noise via the inexpensive mixer’s mic preamp as you boost the input level.

In terms of gain-before-feedback, it actually may be better to use the “mic” level signal. Even with the “trim” or “gain” adjustment at its lowest setting, the mixer’s input still might be designed for a lower signal level than a device like the Shure ULXD4 receiver puts out at “line” level. If there is too much overall gain in the signal path, this could get out of hand and lead to feedback issues!

While some mixers might have a user-selectable “pad,” others only offer a fixed pad on their ¼” inputs only. I would recommend checking the range of input levels for the mixer, and comparing it with the different output signal levels available on a wireless receiver. Also, keep in mind that many other factors contribute to gain-before-feedback, such as the mic capsule being used, the type and placement of loudspeakers, room acoustics, and the distance from the mic to the source. As always, experimentation is key!

I work on an e-commerce site that sells a Shure headphones and Shure microphones (www.infomusicshop.com/shure). Our customers were constantly asking questions about this content. I really like the article about this subject. Thank you very much

One very minor correction and one bit of additional info:
40 dB (regardless of being dBu or dBV) is a ratio of 100 in voltage and 10,000 in power. 60 dB is 1,000:1 and 1,000,000:1 respectively. The nominals that Justin quoted are correct, but the span in differences is even more impressive than the 1,000:1 that he listed. Think of it … 1 million times weaker …

Second, the dBu is a historical normalized voltage agreed on in the 50’s. It is 1 milliwatt into 600 Ohms. This is sqrt(600/1000) ~ 0.775. They are not far apart from each other, 0 dBu is just 2.22 dB weaker than 0 dBV. No real good reason for the difference, but these are the conventions used.

Thanks for the great refresher, Justin. I agree with @Anonymous. Shure is always a great choice.

Consider this an “average” line level signal, as many mixer inputs have an actual clipping level as high as +24 dBu to provide headroom for audio peaks.

Specifying “consumer” line-level in dBV and “professional” line-level in dBu is an industry standard. The Yamaha Sound Reinforcement Handbook is an excellent reference book that contains more information about their origins. With modern audio equipment, the difference really is not significant.

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